506 PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 



mobile is an impossibility. In such, the first portion of the machine, if 

 once set in motion, is to move the second, this the third, &c. the last 

 again the first, without ceasing. The action of the first part of the ma- 

 chine however arrives at the last part greatly diminished by resistances 

 to motion, and from this returns again diminished to the first part, and 

 so on ; the machine, therefore, will soon stop. If then this kind of ma- 

 chine, which only performs its own continuous motion, is impossible, how 

 could any mechanism be found which once moved, would in addition per- 

 form outside work without renewal of power '? That is what the wise 

 searchers for a " perpetual motion" are striving for! A machine in con- 

 tinuous motion itself would be too insignificant for them ; it must be an 

 apparatus that would work incessantly and gratuitously, which need bo 

 set in motiou but once, when motion and work would continue forever. 



As in the foregoing, it has been demonstrated from theoretical me- 

 chanics that a "perpetual motion" is impossible, and as this has also 

 been confirmed by experience, Helmholtz, (1847 — he was not then as yet 

 acquainted with the pertinent works of Mayer and Colding, and only 

 obtained knowledge of that of Joule towards the close of his researches) — 

 deduced from this the theory of the "conservation of energy" by pre- 

 senting the question : " If a perpetuum mobile is necessarily impossible, 

 what are then the relations of the natural forces to one another ? " Helm- 

 holtz points out that if the assumption of the impossibility of a perpetuum 

 mobile is combined with the law set forth by Newton (lGSG), "In every 

 action of a force a similar and opposite reaction is always present," the 

 doctrine of the mechanical equivalence of heat results therefrom. Cold- 

 ing had previously (1813) expressed himself by reversing the above in 

 this wise, that if the proposition maintained by him as to the indestructi- 

 bility and convertibility of natural forces were false, a perpetuum mobile 

 would be possible. Newton's proposition of the equality of action and 

 reaction of a force has become so general that it includes Bernoulli's be- 

 fore-meutioned principle of virtual velocities. We may therefore con- 

 clude that Newton had approached the discovery of the theory of the 

 conservation of energy even earlier, and from a more general standpoint 

 than Bernoulli. 



It has been observed that the term "conservation of force" has in the 

 course of time been replaced by "conservation of energy." Why had 

 the term "force" to give place to "energy" 'I The answer will follow if 

 the meaning of the term "force" is precisely defined, and if the effect 

 or the capability of action of a force — i. e. its "energy" — is not con- 

 founded with the "force" itself, which is considered as the cause of the 

 effect or capability of action. Force is the appellation for every cause 

 which overcomes the property of persistence or the inertness of it body, 

 or endeavors to overcome it; that is, every cause which actually prevails 

 upon a resting body to move, or upon a moving body to rest, or en- 

 deavors to do so. Every force which acts upon a body emanates from 

 some other body. Force is never one-sided in its action, but in the 

 same force with which the first body acts upon the second one this will 



